Water desalination

Abstract

An in situ desalination apparatus comprising a reverse osmosis unit ( 15 ) having a reverse osmosis medium, the reverse osmosis unit in use to be located within a body of water under ambient bio-physico-chemical conditions often different from those at the surface, the unit having an inlet ( 17 ) opening to one side of the reverse osmosis medium, in use the inlet to be located below the upper surface of a body of water, the unit having a concentrate outlet ( 25 ) opening to the one side of the reverse osmosis medium and opening into the exterior of the unit at a position spaced below the inlet to return concentrate into the water body, the unit having a permeate outlet ( 27 ) opening to the other side of the reverse osmosis medium, the permeate outlet communicating with a delivery line extending from the body of water, a pump ( 23 ) between body of water and the reverse osmosis unit and adapted to pressurize the water located at the one side of the reverse osmosis medium.

1. An in situ desalination apparatus adapted for use located in a borehole containing groundwater from a subterranean aquifer and provided with a casing for the borehole, the casing comprising a wall at least a portion of which is screened allowing water to flow therethrough, the desalination apparatus comprising:
 a sealing means for sealing against the borehole casing to separate the borehole into upper and lower portions the casing allowing flow of ground water through the screen into at least the upper portion; 
 a reverse osmosis unit comprising a reverse osmosis medium; 
 an inlet for the reverse osmosis unit located on one side of the reverse osmosis medium, in use the inlet to be located below the upper surface of the groundwater and in the upper portion of the borehole with respect to the sealing means; 
 a concentrate outlet for the reverse osmosis unit opening to the one side of said reverse osmosis medium as the inlet, for delivering concentrate to the lower portion of the borehole with respect to the sealing means; 
 a permeate outlet on the other side of the reverse osmosis medium from said inlet; 
 a delivery line in fluid communication with the permeate outlet in use extending from the body of water; and 
 a pump for delivering groundwater to the inlet; and wherein the sealing means is adapted to allow the apparatus including the sealing means to be removably inserted into the borehole casing, wherein the sealing means is a packer adapted to allow the apparatus to be removably inserted into the borehole casing. 
 
   
   
     2. An in situ desalination apparatus according to  claim 1  wherein the sealing means is expandable from a state receivable within the casing to an expanded state sealed against the casing. 
   
   
     3. An in situ desalination apparatus according to  claim 2  wherein the sealing means comprises an inflatable packer which can be selectively inflated to seal against the casing. 
   
   
     4. An in situ desalination apparatus according to  claim 1  wherein the sealing means seals against the casing to separate the borehole into an upper part wherein the casing comprises a screened wall portion for admitting water from the aquifer and a lower part wherein the casing comprises a screened wall portion to allow the saline concentrate to dissipate within the aquifer. 
   
   
     5. An in situ desalination apparatus according to  claim 4  wherein the casing comprises two screened portions axially spaced along the length of the casing. 
   
   
     6. An in situ desalination apparatus according to  claim 1  wherein the permeate outlet is associated with a pumping means adapted to extract permeate passing through the reverse osmosis medium. 
   
   
     7. An in situ desalination apparatus according to  claim 1  wherein the permeate outlet is vented to the atmosphere. 
   
   
     8. An in situ desalination apparatus according to  claim 1  wherein the pump is a common pump connected to the inlet and the permeate outlet through a set of valves whereby said common pump is able to introduce said water into the inlet and deliver permeate from the permeate outlet through a controlled activation of the valves. 
   
   
     9. An in situ desalination apparatus comprising
 a length of tubular borehole casing adapted in use to be located in a borehole the casing comprising at least a portion of screened wall for allowing the passage of water through the casing; 
 a sealing means for sealing against the borehole casing and dividing the borehole within the casing into an upper portion and a lower portion, the sealing means and borehole casing cooperating to allow flow of ground water through a screened portion into at least the upper portion; 
 a reverse osmosis unit supported within the bore hole by the sealing means the reverse osmosis unit having a reverse osmosis medium; 
 an inlet for the reverse osmosis unit providing communication between the upper portion of the interior of the casing and one side of the reverse osmosis medium; 
 a concentrate outlet for the reverse osmosis unit providing communication between the one side of the reverse osmosis medium and the lower portion of the borehole, wherein the concentrate outlet is controlled by an exhaust valve which is closed upon the pressure at the one side of the reverse osmosis medium falling below a pressure of determined magnitude which is at least equal to the desired operating pressure of the reverse osmosis unit; 
 a permeate outlet for the reverse osmosis unit opening on the other side of the reverse osmosis medium; 
 a delivery line in communication with the permeate outlet extending from the body of water; and 
 a pump for delivering water under pressure from the upper portion of the interior of the casing to the inlet, whereby the pressure differential created across the reverse osmosis medium facilitates reverse osmosis and wherein the tubular borehole casing includes a portion of screened wall in the upper portion of the casing with respect to the sealing means and a screened portion in the lower part with respect to the sealing means, wherein the sealing means is a packer adapted to allow the apparatus to be removably inserted into the borehole casing. 
 
   
   
     10. An in situ desalination apparatus according to  claim 9  wherein the screened wall is continuous. 
   
   
     11. An in situ desalination apparatus according to  claim 9  wherein there are at least two portions of screened wall at axially spaced locations along the length of the casing. 
   
   
     12. An in situ desalination apparatus according to  claim 9  further comprising a groundwater delivery pump for providing a flow of groundwater through a screened portion into an upper portion of the borehole in the casing. 
   
   
     13. An in situ desalination apparatus according to  claim 9  wherein the sealing means is expandable from a state receivable within the casing to an expanded state sealed against of the casing. 
   
   
     14. An in situ desalination apparatus as claimed at  claim 9  wherein the permeate outlet is associated with a pumping means adapted to extract permeate passing through the reverse osmosis medium. 
   
   
     15. An in situ desalination apparatus as claimed at  claim 14  wherein the permeate outlet is vented to the atmosphere. 
   
   
     16. An in situ desalination apparatus according to  claim 9  wherein the concentrate outlet is controlled to maintain pressure of predetermined magnitude sufficient for reverse osmosis. 
   
   
     17. An in situ desalination apparatus according to  claim 9  wherein the sealing means comprises an inflatable packer which can be selectively inflated to provide the sealing against the casing. 
   
   
     18. An in situ desalination apparatus according to  claim 9  wherein the reverse osmosis medium, pump and sealing means together comprise a unit which is removable from the casing. 
   
   
     19. An in situ desalination apparatus according to  claim 9  wherein the casing comprises two screened portions at axially spaced locations along the length of the casing and the sealing means in use engages the inner face of the casing between the two screened portions such that the upper portion communicates with the upper most screen and is sealed from the lower screen. 
   
   
     20. An in situ desalination apparatus according to  claim 9  comprising a borehole in an aquifer comprising a water table, a borehole casing lining the borehole, an assembly comprising the reverse osmosis unit, the pump and the sealing means adapted to be removably inserted in the borehole casing and retained therein by radial expansion of the sealing means.